The invention relates to a metal gasket, in particular a cylinder head gasket for a combustion engine with a sealing plate having a combustion chamber through-hole, and with a deformation-limiting device lying adjacent to the combustion chamber through-hole and a top and bottom layer.
In DE 42 19 709 A1 are described metal gaskets in various embodiments. One of the disclosed gaskets contains a deformation-limiting device which is formed as the crimping-over of an annular portion of the sealing plate at the combustion chamber through-hole. During the crimping process, a part of the annular portion which has a reduced material thickness by comparison with the sealing plate, is laid round over itself so that the deformation-limiting device is formed by a doubling of the reduced material thickness.
If a sealing plate provided in this way with a deformation-limiting device or stopper is used as the middle layer between two cover plates with beads, and the three-layer seal thus formed is pressed together, the pressing forces are transferred in an uneven manner, such that the load alleviation of the cover plates is uneven.
Asymmetrical beads filled with a resin or the like are also generally known (see U.S. Pat. No. 5,582,415).
In EP 0 747 614 A1 is disclosed a metal cylinder head gasket which has two outer cover plates with beads and a support plate disposed between same, which are provided with one or more combustion chamber through-holes. Adjacent to the beads of the cover plates is provided a deformation-limiting device around the combustion chamber through-hole at the supporting plate, which device is provided with rounded portions on the surfaces facing the cover plates.
The object underlying the invention is to create a metal gasket of this type, which with a simple set-up applies uniform pressure and has improved, adaptable deformation behaviour.
This object is achieved according to the invention by the characterising features of the main claim in conjunction with the features of the preamble.
Because the deformation-limiting device is configured as a bead which is symmetrical in respect of the top and bottom layers, in such a way that a protrusion is oriented towards one of the layers and lying opposite a depression facing the other of the two layers is provided, which is surrounded by two raised portions protruding opposite the surface of the sealing plate, a filling being accommodated in the depression, the stopper which is usually provided in prior art can be dispensed with or the stopper layer is replaced by the symmetrical bead. Furthermore, uniform compression is possible and the bottom and top layers are uniformly relieved of pressure. Through the special shape of the bead in conjunction with the filling, it adapts to the engine topography during fitting, being adjustable in compression to a preset degree.
Through the measures quoted in the subordinate claims, advantageous developments and improvements are possible.
It is particularly advantageous that the protrusion of the bead is provided with a radius or a convexity, by which means the surface pressure can be increased. By pre-determining the amount of the filling in the depression or respectively the width and height of the filling and/or through the size of the radius, which can change after pressing into a straight line, deliberate pressure control can be undertaken and the adaptation to the engine can be set, by which means its dynamics and the sealing gap oscillations can be reduced.
Altogether the symmetry of the bead produces a uniform distribution of the force from the beads of the bottom and top plates.